The following descriptions and examples do not constitute an admission as prior art by virtue of their inclusion within this section.
Drilling tools, such as drilling motors, may be used to provide rotational force to a drill bit when drilling earth formations. Drilling motors used for this purpose may be driven by drilling fluids pumped from surface equipment through a drill string. This type of motor may be referred to as a mud motor. In use, the drilling fluid may be forced through the mud motor, which may extract energy from the flow to provide rotational force to a drill bit located below the mud motor. A mud motor may include a positive displacement motor (PDM) or a turbodrill.
For some drilling tools, radial bearings may be used to prevent vibration of a shaft within the drilling tool due to misalignment. In addition, the radial bearing may be used to mitigate effects of side loads in the drilling tool during directional drilling. Each radial bearing may include a sleeve mounted to the shaft so that the sleeve and shaft rotate together. Each radial bearing may also include a bushing disposed coaxially around the sleeve, where the bushing may be configured to frictionally engage an inner wall of a housing of the drilling tool to prevent the bushing from rotating and to allow the sleeve to rotate within the bushing.
Friction in contact areas of the radial bearing may generate increased levels of heat during rotation of the shaft. High operating temperatures often lead to physical failure of radial bearing components. While a flow of drilling fluid through the radial bearing may at least partially inhibit damage to the bushing and/or the sleeve, drilling fluid which passes too quickly may have insufficient time to dissipate the heat produced in the radial bearing.
At elevated temperature levels, frictional welding may occur between the bushing and the sleeve, causing the rotation of the shaft to be arrested. Further, at elevated temperature levels, coatings along the bushing and/or the sleeve, such as those made of an elastomeric material, may begin to crack. Due to certain designs of radial bearings, the drilling fluid may have insufficient time to remove abrasive particles in the contact areas, such that the abrasive particles may rip or cause a chunking of the coatings on the bushing and/or the sleeve. As a result, drilling tool components positioned near the radial bearing may experience increased erosion due to the quick-passing drilling fluid.
In addition, continuous friction in contact areas of the radial bearing may generate excessive wear of the radial bearing components. For example, coatings of the bushing and/or the sleeve may wear out, leading to a wearing out of the bushing and/or the sleeve themselves. If components of the radial bearing are sufficiently worn, then the shaft may be positioned off-center within the drilling tool. The off-center shaft may experience increased vibration and the misaligned system may contact against the housing of the drilling tool. In such a scenario, the shaft may incur damage and eventually fracture.